The present invention relates to a method and apparatus for enhancing the quality of continuously cast steel billets, and which may be employed in association with the conventional continuous casting operation.
During the vertical continuous casting of steel billets, the billet advances from the caster in a downward direction and then gradually curves to a horizontal direction as it cools. When casting products of round cross section, the solidification process is relatively uniform and the cast metal experiences isotropic stresses that are easily relieved during the subsequent cooling process. However, when casting square or rectangular billets, certain anisotropic stresses occur in the cast metal during solidification and cooling, and these stresses may be significant and can cause the sharp corner edges of the cast metal to crack during the initial rapid cooling process. These cracks resemble V-like stripes on the edges, and they are commonly called chevron cracks. Such chevron cracks typically are 1/16 to 1/4 inch deep. While the development of chevron cracks is more prevalent in the case of vertical continuous casting, it is often a problem in a horizontal continuous casting operation.
The quality of the cast steel billet is determined in part by the number, density, and average depth of the chevron cracks, and these characteristics of the cracks are affected by the content of carbon and alloying elements in the steel. Billets with high carbon content exhibit more and deeper cracks, while high alloy steels exhibit fewer and more shallow cracks, or perhaps no cracks at all.
Quality control inspection of continuously cast steel billets is a difficult procedure, and the inspection cannot now be easily accomplished visually while the billet is hot. In addition, there are four or more corner edges to visually inspect while the billet is advancing, and as a result, visual inspection is now accomplished only after the billets are cooled and they can be scrutinized and handled for further processing as may be required to remove the cracks.
The U.S. Pat. No. 3,596,047 to Maniero discloses a prior procedure for removing cracks from the surface of a metal workpiece, and wherein one or more electric arcs engage the surface of the workpiece. The arcs cause the surface to melt and heal the cracks. This procedure however is not seen to be able to closely control the applied level of heat, and in addition, the workpiece must be electrically grounded which increases the complexity of the apparatus.
It is accordingly an object of the present invention to provide a method and apparatus for efficiently enhancing the quality of continuously cast steel billets, and which effectively removes and heals the cracks which may be present along the corner edges of the billet.
It is also an object of the present invention to provide a method and apparatus of the described type, which is able to closely control the amount of heat applied to the corner edges of the workpiece, and which does not require that the workpiece be electrically grounded. It is still another object of the present invention to provide a method and apparatus of the described type which may be employed in conjunction with the continuous casting operation, and so that the billet may be hot during the quality enhancing operation to thereby minimize the heat energy required.